Process for alkylating aromatic compounds

ABSTRACT

THIS DISCLOSURE IS CONCERNED WITH A PROCESS FOR ALKYLATING AROMATIC COMPOUNDS IN THE PRESENCE OF AN UNSUPPORTED CATALYST HAVING AT LEAST 2 MOLS OF A TITANIUM TETRAHALIDE PER MOL OF A DIORGANOZINC COMPOUND.

United States Patent Oihce 3,641,178 Patented Feb. 8, 1972 US. Cl. 260-671 P 10 Claims ABSTRACT OF THE DISCLOSURE This disclosure is concerned with a process for alkylating aromatic compounds in the presence of an unsupported catalyst having at least 2 mols of a titanium tetrahalide per mol of a diorganozinc compound.

It is known to alkylate aromatic compounds by a Friedel Crafts reaction in the presence of a catalyst such as Lewis acids, i.e., AlCl FeCl etc. Further, it is known to make an alkylating catalyst from a metal alkyl compound and a metal halide supported on a solid carrier, such as alumina ('U.S. 3,031,514). The latter catalyst shows a wide range of activities, such as alkylation, isomerization, disproportionation and polymerization of unsaturated hydrocarbons. This leads to the formation of by-products simultaneous with the alkylation process. In certain instances, however, the substantial formation of these by-products is undesirable.

It has now been discovered that the alkylated aromatic compounds can be provided with little or no side reactions by using an alkylating catalyst which does not show such a wide range of activities. Thus in accordance with one embodiment of this invention, an aromatic compound is reacted with an alkylating agent in the presence of a certain catalyst but in the absence of a solid carrier as a support for the catalyst.

Any aromatic compound which is capable of being alkylated is suitable for this invention. These aromatic compounds are generally liquid hydrocarbons having a replaceable nuclear hydrogen. This includes, among others, the following:

The alkylating agents in this invention are certain alkenes or alkyl halogenides. An alkene, if employed, must have at least 3 carbon atoms, e.g., 3 to 18 carbon atoms, since ethylene is not satisfactory for the present invention. The alkenes can be straight or branched chained and acyclic or cyclic olefins, diolefins or thiolefins and the following, among others, are suitable:

propylene 4-methy1 heptene-l l-butene S-methyl hexene-l 2-butene S-methyl heptene-l isobutene 3-ethyl bu-tene-l l-pentene 3-ethyl pentene-l 2-hexene 4-ethyl hexene-l cyclohexene 3,3dimethyl butene-l l-octene 3,3-dimethyl pentene-l l-decene 3,4-dimethyl pentene-l butadiene isoprene 1,5-octadiene 1,5,9-dodecatriene styrene alpha-methylstyrene allyl cyclopentane vinyl cyclohexane Suitable alkyl halogenides, when employed, are those containing a C to C alkyl group, and wherein the halogen atom is chloro, bromo or iodo, Compounds within this group include, among others, the following:

ethyl chloride n-butyl chloride n-propyl chloride isopropyl chloride t-butyl chloride 2-ethylhexyl chloride The alkylating agent can also be a mixture of any of the alkenes and alkyl halogenides set forth above. The mol ratio of the aromatic compound to alkylating agent is generally from about 10:1 to 1:1 and depends on the nature of the desired end products. An excess of aromatic compound is conducive to monosubstitution.

The catalyst combination is a mixture of a diorganozinc compound (R Zn) and titanium tetrachloride (TiCl or titanium tetrabromide (TiBr It is critical to use both compounds in this invention since the results are not satisfactory if either the aforementioned zinc compound or halide compound is used alone. Furthermore, inferior results are obtained if an organozinc halide compound (RZnX) is substituted for the diorganozinc compound in the aforementioned mixture.

The diorganozinc compound for the present invention has the following generic structure:

octadecene 2,3-dimethyl butene-Z 3-methyl butene-l 3-methy1 pentene-l 3-methyl hexene-l 3-methyl heptene-l 4-methyl pentene-l 4-methyl hexene-l t-butyl bromide isopropyl bromide n-propyl iodide isopropyl iodide partly halogenated parafiin diphenyl zinc ditolyl zinc dinaphthyl zinc diethyl zinc dibutyl zinc dihexyl zinc In this invention, titanium tetrachloride is usually used as the other compound in the catalyst combination. However, titanim tetrabromide can also be used. Other titanium halides, such as, titanium trichloride and titanium tribromide are not satisfactory. The molar quantity of titanium tetrachloride can be from about 2 to 6 times the molar quantity of R Zn. The yield is not sufficient if 1 mol titanium tetrachloride is employed with 1 mol R Zn. Higher amounts than 6 mols titanium tetrachloride with 1 mol R Zn may be used, but are uneconomical and unnecessary. Generally about 0.1 to 7.0 mols of titanium tetrachloride are used per mols of alkylated product to be expected.

The catalyst combination of titanium tetrachloride and R Zn may be formed by any satisfactory method. A solvent that is inert to these compounds, is frequently employed, such as hexane or a petroleum fraction. In fact, the aromatic compound to be alkylated may be used as the only solvent. In general, the alkylation can be conducted over a wide temperature range, e.g., about 10 C. to 100 C. The reaction can be initiated at room temperature or lower and the temperature rises since it is mostly exothermic. However, the reaction can also be initiated at a higher temperature, e.g., 50 or 100 C. The upper temperature limit is determined by the boiling point of the lowest-boiling component in the reaction mixture which is dependent upon the pressure employed in the reaction mixture. The pressure can also vary over a wide range including, without limitation, atmospheric pressure and superatmospheric pressure in an autoclave. Generally, the components can be added to the reaction vessel in any order and the alkylated aromatic end product can be recovered b an appropriate procedure.

An important feature in the present invention is that the catalyst is unsupported, i.e., without a solid carrier as a support.

Thus in accordance with this invention, an alkylated aromatic compound is provided without the extensive formation of isomers and polymers. The uses of these compounds are known in the art. For instance, the reaction product of benzene and propylene is an intermediate in the preparation of phenol and acetone (cumene process). The dialkylation product of p-xylene and propylene can be oxidized to pyromellitic anhydride, which is a basic material for certain thermostable polymers. The monoalkylation product of m-xylene and propylene, 1,3- dirnethyl-Z-isopropylbenzene, can be used as an intermediate in the preparation of 2,6-dimethylphenol, which is the raw material for poly-2,6-dimethylphenylene oxide.

The following examples are submitted to illustrate but not to limit this invention. Unless otherwise indicated, all parts and percentages in the specification and claims are based upon weight.

EXAMPLE I Diethyl zinc (0.01 mol) and titanium tetrachloride (0.02 mol) were dissolved with stirring in 6.4 mols dry benzene with oxygen and water being excluded to form a dark colored precipitate. After 30 minutes stirring, the temperature was raised to 70 C. and 1 mol propylene gas was then introduced. The reaction mixture was next washed with 4 N HCl and water to remove the catalyst. After distilling off the excess of benzene, the residue was analyzed by gas chromatography. The degree of alkylation was 89.2% with 71% of the propylene being converted into isopropyl benzene, 17.2% into diisopropyl benzene and 1% into triisopropyl benzene.

This example demonstrates that an alkylated aromatic compound can be provided without substantial isomerization and polymerization.

EXAMPLE II Into 16 cc. m-xylene, 246 mg. diphenyl zinc and 428 mg. titanium tetrachloride were dissolved with stirring and with oxygen and water being excluded with the mol ratio for the catalyst being 1:2. At about 70 C., 18.9 g. propylene was added dropwise to the reaction mixture by means of a carbon dioxide-acetone cooler. After treating the reaction mixture as described in Example I, the residue was analyzed. The results were: 20% of the m-xylene was converted into dimethylisopropyl benzene in which 80.6% was the 1,3-dimethyl-4-isopropyl benzene; 63% of the m-xylene was converted into the dimethyl-diisopropyl benzene in which 76.7% was 1,3-dimethyl-4,6-diisopropyl benzene; and 3.7% of the m-xylene was converted into dimethyl-tri-isopropyl benzene in which 86.8% was the 1,3-dimethyl-2,4,6-triisopropy1 benzene.

EXAMPLE III Diethyl zinc (111 mg.) was dissolved in 22 cc. p-xylene as described in Example I. Thereafter titanium tetrachloride (340 mg.) was added. The mol ratio for the catalyst was 1:2. At 8090 C. 17.3 g. propylene gas was introduced. After treating and analyzing as described in Example I, it was found that all p-xylene had been converted with 9.5% as 1,4-dimethyl-2-isopropyl benzene and 90.5% as 1,4-dimethyl-2,5-diisopropyl benzene.

4 EXAMPLE 1v Diphenylzinc (41 mg.) dissolved in 5 m1. m-xylene and titanium tetrachloride (79 mg.) dissolved in 0.5 ml. hexane were injected in a dry oxygen free stainless steel glass-lined autoclave equipped with a magnetic stirrer. After a half hour stirring, 55 ml. m-xylene were added and propylene gas was pressed into the autoclave up to 9 atmosphere pressure. The ratio of propylene to mxylene was 1:10 in order to promote the formation of monoalkylation products.

The autoclave was stirred and heated during 5 hours at exactly 50 C. After cooling, the reaction mixture was treated as described in Example I and fractionated. The distillate, boiling from 76-95 C. at 12 mm. vacuum, was analyzed by gas chromatography. It contained 77% monoalkylation products, calculated on the propylene added, consisting of 17% l,3-dimethyl-2-isopropylbenzene, 73% 1,3-dimethyl-4-isopropylbenzene and 10% 1,3- dimethyl-S-isopropylbenzene. The distillation residue, consisting of dialkylation products, amounted to about 2%.

It is evident from this example, that no substantial isomerization took place because 1,3-dimethyl-2-isopropylbenzene cannot be obtained with conventional alkylation catalysts, unless in very small amounts 2%), due to product isomerization.

EXAMPLE V To investigate the amount of product isomerization a mixture of 117 m. mols monoisopropyl-m-xylenes was heated in an inert atmosphere during 5 hrs. at 80 C. in the presence of 1 mol percent diphenylzinc and 2 mol percent titanium tetrachloride in hexane. After treating the reaction mixture as described in Example I, the composition was determined by gas chromatography. The results are shown in Table A.

TABLE A Wt. percent of isomers Before After Isomer mixture heating heating 2-isopropyl-1,3-dimethylbenzene. 16 15 4- sopropyl-1,3-dirnethylbenzene 72 73 5-1sopropyl-1,B-dimethylbenzene 12 12 This example demonstrates that the catalyst system of 1:2 diphenyl zinc to titanium tetrachloride shows no substantial tendency for product isomerization.

EXAMPLE VI EXAMPLE V11 In order to demonstrate the low disproportionation tendency of the catalyst system, a mixture of 21.7 g. phenyldodecane isomers was heated in 46 ml. benzene during 3 hours at reflux temperature in the presence of 1 mol percent diphenylzinc and 2 mol percent titanium tetrachloride. After providing the reaction products as described in Example I, the amount of isomers was determined by gas chromatography. The results are listed in Table B.

TABLE B TABLE D Wt. percent of isomers Ratio by weight Molar ratio Percent Before After absorbed, Yield, Isopropyl Diisopropyl Isomers heating heating 5 Benzene Propylene H; mono l benzene benzene 2-phenyldodecane 47 44 3.2... 1 100 46. 6 3. 2 1 B-phenyldodecane. 20 20 4.8. 1 96 52. 5. 4 1 4,5,6-pheny1dodecane 33 36 6.4. 1 100 57. 8 6. 3 1 q 3 1 80 4L 4 9. 1 1

Isopropyl benzene.

This example shows that no substantial disproportionation took place.

EXAMPLE VIII The procedure of Example I was repeated but with various molar ratios of diphenyl zinc to titanium tetrachloride for alkylating benzene with propylene. The temperature was 70 C. The reaction time was 2 hours. The molar ratio benzene to propylene was 32:1. The results are shown in Table C. A

TABLE 0 Percent reaction product relative to absorbed 0 H M01 percent 1 Percent absorbed, Monosub- Disubsti- Diphenyl zinc T1014 0 H; stitution tution l The quantity of catalyst is calculated on the quantity of propylene.

The procedure was repeated substituting diethyl zinc for diphenyl zinc. The results were comparable.

This example demonstrates that it is critical to use a combination of diorganozinc compound and titanium tetrachloride since the use of either one alone did not The procedure was repeated with diethyl zinc and titanium tetrachloride (1 mol percent:2 mol percent) with a molar ratio of benzene to propylene of 6.4:1. This resulted in 100% of the propylene being absorbed and 71% of the end product was isopropyl benzene.

According to this example, it is preferred to use a ratio of aromatic compound to al-kylating agent of between 8:1 and 10:1 when mainly monosubstitution is Wanted.

EXAMPLE X Benzene, toluene, m-xylene and p-xylene were alkylated with propylene in accordance with the procedure described in Example I.

Alkylating benzene with propylene in the presence of diphenyl zinc and titanium tetrachloride at a ratio of 1:2 mol percent provided the following: 58.2% of' the benzene reacted to form 32% isopropyl benzene, 30% ortho-, metaand para-diisopropyl benzene and 38% three isomeric triisopropyl benzenes.

Alkylating toluene with diethyl zinc and titanium tetrachloride at a ratio of 0.25 :0.50 mol percent, caused 90.5% of the toluene to be reacted. About 20% methyldiisopropyl benzene and 80% methyl-triisopropyl benzene were obtained.

The procedure was repeated with m-xylene and a catalyst containing diphenyl zinc and titanium tetrachloride at a ratio of 0.25 :0.5 mol percent and 86.7% of the mxylene was alkylated. The product consisted of 23% monoalkylation product (80% being 1,3-dimethyl-4-isopropyl benzene) and 72.5% dialkylation product (76.7% being 1,3-dimethyl-4,6-diisopropyl benzene) and 2.5% trialkylation product. The total yield of 1,3-dimethyl- 4,6-diisopropyl benzene relative to m-xylene was 48%.

The procedure was also repeated, alkylating p-xylene with propylene at a temperature of 8090 C. with a reaction time of 1.5 hours. The results are indicated in Table E.

TABLE E Percentage Mol ratio Percentage total yield of M01 percent Percent reacting to- 1,4-dimethyl- Proalkylated 2,5-diisopropyl B2211 RzZn TiClt p-Xylene pylene xylene Mono 1 Di a benzene Diphenyl 0. 25 0. 5 1 2 80 20 80 62 Diethyl 0. 6 1. 0 1 4 100 9. 5 91. 5 90 D 0. 25 0. 5 1 4 63 42. 5 57. 5 34. 5 0. 25 1. 0 1 4 76 28 72 52 0. 125 1. 0 1 4 20 74 25 5 1 Monosubstituted 2 Disubstituted.

provide an alkylated aromatic reaction product. This example also demonstrates that it is critical to have a molar ratio of at least 2 for the titanium tetrachloride to the diorganozinc compound in order to form the aforementioned reaction product.

EXAMPLE IX Example I was repeated with various molar ratios of benzene to propylene with a catalyst combination of 1% titanium tetrachloride and 0.5% diphenyl zinc based on propylene. The temperature was 70 C. The reaction time was 2 to 2 /2 hours. Table D shows the results.

The procedure of Example I was repeated to react benzene with l-octadecene at a mol ratio of 10:1. The catalyst was diethyl zinc and titanium tetrachloride. The temperature was about C. and the reaction time was 3 hours. The results are listed in Table F.

TABLE F Gone. in mol (percent) 1 Oetadecene, Isomer composition percent which EtzZn TlGh reacted Z-phenyl 3-phenyl 4-phenyl 5+6-pheny1 1 Calculated on octadecene.

Similar results were also obtained by repeating the procedure with diphenyl zinc instead of diethyl zinc.

This example shows that satisfactory results were obtained by alkylating with a long-chain olefin using proper Having set forth the general nature and specific embodiments of the present invention, the true scope is now particularly pointed out in the appended claims.

What is claimed is:

catalyst concentrations. 1. A process which comprises alkylating an aromatic EXAMPLE XII compound with an alkylating agent selected from the group consisting of an alkene having at least 3 carbon Benzene was also alkylated with various alkyl halogeatoms and an alkyl halogenide wherein the alkyl group has nides by following the procedure of Example I. Both 2 to carbon atoms and the halo group is chloro, bromo P Y Zinc and diethyl Zinc Were used a he Organoor iodo in the presence of an unsupported catalyst; said zinc compound. The ratio of benzene to alkyl halogenide catalyst consisting of (A) titanium tetrachloride or tita- Was The ratio of Catalyst R2211 t0 titanium tet anium tetrabromide and (B) a diorgano compound having chloride was 1 mol percent:2 mol percent based on benth tr t zene. The temperature was 80 C. Table G lists the satisfactory results. RZn-R TABLE G Diphenylzinc plus Diethyl zinc plus Reaction 'IiCh Reaction T1014 time in time in Alkyl halogenido hours Mono Di hours Mono 1 Di 2 Isopropyl chloride 6 23. 5 1. 6 5 52 17 Tertiary butyl chloride 0. 5 54 28. 6 0. 5 s2 4 1 Monosubstituted. 2 Disubstituted.

Comparable satisfactory results were noted when the prowherein each R is independently selected from a hydro cedure was repeated with isopropyl bromide and tertiary carbon group having 1 to 18 carbon atoms; said catalyst butyl bromide. having a mol ratio of A :B of at least 2:1.

It is manifest from this example that an alkyl halogen- 2. The process according to claim 1 in which the alkylide can be used as the alkylating agent in this invention. ating agent is an alkeneI l 1 h h h 1k 1 3. The process accor ing to c aim in w ic t e a y EXAMPLE XIII ating agent is an alkyl halogenide. The procedure of Example VI Was r p eXcept that 4. The process according to claim 1 in which the catathe diethyl zinc is replaced with ethyl zinc chloride. The lyst tains titaniu tetrachloride, results are as follows: the alkylation degree was 43% and 5. The process according to claim 1 i hi h h mthe reaction product contained 90% monoalkylation and lyst t ins titanium tetrabromjde. 10% dialkylation products. r 6. The process according to claim 1 in which the cata- Examples VI and XIII show the superiority of using a lyst contains diethylzinc diol'gano Zinc Compound rather than an Orgaflo Zinc halide 7. The process according to claim 1 in which the catacompound in combination with titanium tetrachloride. lyst contains diphenyl zinc.

EXAMPLE XIV 8. The process according to claim 1 in which the alkylatlng agent is selected from the group consisting of P f of Example I was repeated except that propylene, l-butene, Z-butene, isobutene, l-octene, l-octathe titanium tetrachloride was replaced indepen decene, isopropyl chloride, isopropyl bromide, tertiary with titanium trichlorlde. No alkylation was obtained. butyl chloride and tertiary butyl bromide coinpzmng Examples 1 XIV 15 appaient that 9. The process according to claim 1 in which the aro- Superlor results are achleved 1f the ,ilorgano Zmc i matic compound to be alkylated is selected from the group pound is used with titanium tetrachlorlde rather than with consisting of benzfine, mdwlene, p xylene and toluene lltamum mchlonde- 10. The process according to claim 1 in which the alk- AM LE XV ylation is conducted at a temperature between about 10 C. and 100 C. The procedure of Example IV was repeated using 'diethyl zinc (0.5 mol percent) and titanium tetrabromide References Cited (1.0 mol percent). The reaction mixture was held at 80 C. during 5 hours and 59% of the propylene was con- UNITED STATES PATENTS verted to monoalkylation prod s. 2,721,189 1-0/ 1955 .Anderson et al. 260-671 C A gas chromatographic analysis of the distillate shoWe 3,031,514 4/1962 Kosmin 260671 C the presence of about 9% l,3-dimethyl-2-isopropylbenzone, 77% 1,3-dimethyl-4-iso-propylbenzene and 14% CURTIS *R. DAVIS, Primary Examiner l,3-dimethyl-S-iso-propylbenzene. The distillation residue amounts to about 2%. CL

This example demonstrates satisfactory results when C titanium tetrabrgrpigle is employed in the catalyst.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 41,17 Dated February 8, 1972 Inventor(s) Henricus Geradus Josef Overmars et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 61, "thiolefins" should be triolefins-;

Column 2, line 53, "titanim" should be -titanium--;

' Column 7, line 31, Table G, "6" should be 5-.

Signed and sealed this 13th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOT'I'SCHALK Attesting Officer Commissioner of Patents 

